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Can a helicopter's main rotor mince a human?
Prompted by one of the answers to a prior question of mine regarding a scenario involving a helicopter mincing someone with its main rotor in flight:

...I suspect having a human body come in to direct contact with the rotor disk 1) would not “finely mince” a person but instead cause severe blunt force trauma followed by flinging the body or body parts from the disk like a rag doll. -Carlo Felicione

Can a typical full-size helicopter (the linked question was asking primarily about an S-92/CH-148-family copter, but answers regarding any reasonably-typical helicopter are fine) mince a typical adult human with its main rotor at typical inflight main-rotor speeds?

I'm tempted to say: "Don't try this at home!" ;-) But honestly: I know cass where people lost fingers hitting the rotor of a model helicopter, event if that was "just" made of balsa wood and not being sharp at all.

@Vikki This doesn't sound like an aviation related question, it's more like a William Osman video title.

It's neither minced nor blunt force trauma. It's more like being chopped by a sword which is neither like being minced by a blender nor like being hit by a baseball bat.

I suspect that, to finely mince a person, you'd need some sort of mechanism to slowly feed them into the rotor disk.  Hang on, I'll just run up FreeCAD...

Dead is dead, does it really matter whether you're chopped into two pieces or 100?

+1 just for "(the linked question was asking primarily about an S-92/CH-148-family copter, but answers regarding any reasonably-typical helicopter are fine)", and upvote for every horrifyingly reasonable and detailed answer too, i.e., all of them.  (And for the comment "Is that also true for the main rotor, though?".)   I know little about helicopters but I've learnt a great deal about helicopter people from this question.  A quiet backwater of cynical sanity.  (I know, I sound sarcastic maybe.  I don't mean that, I assure you.   This is a great question and answers.  What SE is all about!)

@U.Windl does a model helicopter's rotor rotate faster than a real one?

The 1982 fatal accident during the making of 'Twilight Zone: The Movie', although that helicopter's  tail rotor assembly had separated and it was in uncontrolled descent.

@lessthanideal: Full disclosure, I'm not a pilot (the closest I've ever been, or likely will ever be, are paper airplanes and KSP).

U. Windl - even the smallest particle can do great damage at great speed

Barmar - If you are the victim, is does not matter, however, this is probably from the standpoint of the person who has to clean up the mess, in which case it does matter, especially if you are trying to hide the body parts...

Minced could be closer than blunt force trauma, but neither is really going to be a great description.
If decapitation is possible as @filo points out in the comments, we're not talking mere blunt-force trauma. Cutting into smaller pieces is partly a matter of feed rate. Someone falling from just above into a blade would be fed through quite slowly and end up in a state closer to "minced" than the image conjured up by blunt force trauma, which implies (largely) intact. But it's still not really mincing, even though that kind of speed there will be a lot of loose little bits flying around.  Of course some of the bigger body parts will be flung away, especially if they enter the disc near the blade tips.  Conversely falling into the blades above the fuselage would constrain the remains allowing for more chopping.
"Shredded" might be the best word.

Decapitation is possible.  Read up on the Vic Morrow case.  Wiki: "Morrow [was] decapitated and mutilated by the helicopter rotor blades..."

@TonyEnnis,yes, that's the same case that I credited filo with finding (I had read about it before)

Decapitation is possible. This medical peer-reviewed article:
https://link.springer.com/article/10.1007/s12024-015-9721-5
is a forensic study on an helicopter accident. Please note: it has heavy graphic content.

@EarlGrey like Tony you may have missed the meaning of my use of "if" - not a conditional but "accepting that".  I'm wondering whether this a mainly a British usage though the discussion at English.se doesn't suggest so.  It' smight also be a little dated, and anathema to programmers

(Freely-available copy of the article linked by @EarlGrey, for the benefit of readers who don't have a subscription to Forensic Science, Medicine, and Pathology.)

Note that filo's comment's apparently been deleted, so it's not particularly useful to link it in the answer.

Mince:

Cut up or grind (food, especially meat) into very small pieces, typically in a machine with revolving blades.

Blunt force trauma:

Injuries resulting from an impact with a dull, firm surface or object.

Helicopter blades are neither sharp enough, nor spinning rapidly enough to cause the sort of fine mincing you might get with a food processor, nor are they simply a "dull, firm surface."  There is a lot very severe damage possible to the body in between "blunt force trauma" and being "minced", but I don't think you will get a detailed answer until they make a "chicken gun" for human cadavers and run some actual tests.

I assume that there have been lots of accidents in that direction and probably accident reports. In the frame of this question there isn't really a need for testing of the unknown

@CarlBerger, I agree, that part of my answer was facetious.

@CarlBerger I would disagree with your assumption as it is baseless since you have no citations. Purposes for such testing could include determination if such a death was accidental or intentional, and if accidental, how it happened and how it can be prevented.

@user3481644 ah well sure you can disagree, if you want. However.. it's common knowledge that aviation is strictly controlled (in US, Europe etc anyway), and accidents are reported & listed in an effort to increase safety.

@user3481644 Just because I didn't cite the data base, doesn't make my statement dismissable. But since you asked, simple google-fu helps: "data base of aviation accidents" leads eg to https://www.ntsb.gov/Pages/AviationQuery.aspx, listing 10488 helicopter accidents and 1038 fatal ones. Other people have analyzed similar data bases & written reports: https://www.unboundmedicine.com/medline/citation/8216149/Helicopter_rotor_blade_injury:a_persistent_safety_hazard_in_the_U_S__Army

@CarlBerger - My disagreement is about your assertion that "there isn't really a need for the testing of the unknown".

@user3481644, fundamentally I agree with your statements, but what is there to learn by testing that isn't intuitively obvious?  (that a rotor blade will mess you up bad...)

@MichaelHall Forensic studies are conducted to learn details about how people are killed (among other things). If someone were to be chopped and foul play were suspected, the forensics experts would look over what's left and attempt to determine what happened. I've seen dramatisations of bashing fake human heads to see what splatter patterns are created. Such a study (with helicopters) might lead to determine if the victim was clumsy or pushed.

@user3481644, I think you over estimate the number of instances where someone is killed by a rotor blade and actual forensic investigation is needed to understand "why" or "how" it occurred...

It will absolutely cut you to pieces. In fact, there are documented cases of rotor disks flexing enough to cut their way through the cockpit. That's why helicopter helmets are very heavy and uncomfortable, they are rated to take a hit and (potentially) survive it. But having seen helmets that have taken a hit, I can't picture it being survivable. (former helicopter crew member)

Have a read here:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8574166/
"A Case of Penetrating Head Wound Due to Helicopter Rotor Blade Injury in a 34-Year-Old Naval Helicopter Pilot Who Returned to Active Service 5 Years Later"
The primary helicopter pilot was a tall man. He raised his head into the tail rotor tunnel and was hit when he left the cockpit to check the refueling process. Despite being cut by the rotating blade, the helmet had a protective effect, preventing fatal injuries.
it (sometimes) works!

@EarlGrey -- astoundingly flawed logic (mostly likely an inadvertent error on author's part) shown in following sentence from above link ("Discussion" section) : "This shows that ground crews still have nearly a 15% chance of head injury when performing ground tasks."

Into a few pieces, sure...  But finely "minced"?

@quietflyer I did not go past the abstract, so I could not enjoy the statistic extrapolation :D . I trust doctors for their cases-by-cases knowledge, I let statistics to (other) professionals ;) .

@EarlGrey Note that this injury was caused by the tail rotor, not the main rotor: "causing the right side of his helmet to be hit by the tail rotor"

"Mince" implies multiple strikes -- and really, more than just two or three.  The distance between each main rotor blade of a full-scale (manned) helicopter suggests that multiple strikes from the main rotor blades are unlikely.  The body would likely be thrown clear during the first few strikes.  Therefore, regardless of whether the nature of the injury from a single strike would be better described as "cutting / slicing", "blunt force trauma", or something in between, the answer to the actual question is "no".
(The number of rotor blades could have some influence on the answer though-- )

A bunch of good points are being brought up in the comments.
First to point to the differences between the tail and main rotors, despite being locked through the transmission and rotation in synchrony (except when pedals are depressed) the speed of rotation and angle of incidence between the two are quite different.  The tail rotor is balanced to only counter the rotational effects of the main disk, not provide the lifting force for the helicopter.  So any thoughts of an equal comparison between the two is not appropriate.
Now for the ideas about the main rotor system, there is certainly a difference in speed between the center of the rotor and the tips, with the tips traveling at a speed somewhere on the order of .6 mach.  Depending on the position of the collective the angle of incidence of the main rotors is changed. A worst case scenario could be achieved through a horizontal blade angle at time of incident.
Having seen 2 helicopter flight helmets which were struck by the main rotor in my time as a flight medic I can say that the mechanism of injury is certainly severe enough to result in clean cuts to unprotected human anatomy.  This is also in line with the actual fatalities that have occurred from contact with the rotor system.
The speed of the blade compensates for the perceived dullness of its leading edge. Try pressing your finger against a sharp knife, versus dragging it down one.  If you dont believe that the edge is relevant (since its too sharp compared to a rotor) maybe try an axe, since they are honed to being roughly 2x as blunt as a knife. if you cant draw blood on the axe, move your finger quicker, im sure it will feel just like a razor blade, from personal experience.

A friend who served as a helicopter repair station crew chief in Viet Nam says that will happen if a human walks into the tail rotor of a Huey. He himself heard the sound of a human skull getting buzzed to pieces in this way.

Is that also true for the main rotor, though?

It depends on how the body came into contact. If slowly, then it could since there isn't enough mass to stop the rotors. If it was in flight and someone jumped on to it, well, that will require a very specialized test.

@Vikki Isn't it mainly about the "impulse divided by area" (basically mass and speed of the rotor divided by the impact surface)? So the main rotor may be "less sharp than the tail rotor, but the mass should compensate that easily. Maybe someone can impress us with realistic numbers...

@U.Windl I could be wrong, but I thought that the tail rotor and main rotor are usually mechanically linked through a geared shaft.  So if your unfortunate head tries to slow down the tail rotor, it also has the inertia of the main rotor to deal with.

@WayneConrad I could be wrong, but it is my understanding that the tail rotor speed can be adjusted to change the direction the aircraft is facing.

@user3481644 I believe that the tail rotor pedals change the pitch of the tail rotor blades, in a similar mechanism that the main rotor's collective control uses.  The tail rotor's RPM remains proportional to the main rotor's RPM.

ah well. not sure how much this has to do with aviation, but here it goes..
Hitting the rotor tip of a modern Helicopter:
Rotor tip speed is usually designed to be slightly below the speed of sound. Let's find something we can compare it to: a 0.45 ACP bullet is also blunt and subsonic maybe traveling at similar speeds. I have yet to hear of that story where a person got a blunt force trauma when shot by a 0.45. I'd assume the way a helicopter blade interacts with a body will be somewhat similar, just a lot larger and more powerful..
Hence. You won't get a heap of finely minced meat, but likely a few chops. The body won't be thrown around away by "blunt force". The question apparently was addressed already and some people have run simulations on it. For the less faint hearted, here's a visualization of the the 100% accurate simulation:
www.youtube.com/watch?v=VDcDQX7TjhE
I also don't buy that the helmets will withstand much. If you move very slowly, and the first strike is only grazing, then maybe the person realizes soon enough what's going on - else it's a (subsonic) cannon ball to the head.
Hitting the rotor close to the hub:
There seems to be a non-minced case from the early days of helicopter development:
www.youtube.com/watch?v=ixDn8Ak4kz8

A nice animation, but not really a physics simulation.

Well it is  a physics simulation in the sense that physics simulations are also just  mathematical models that approximate the physics. The result is always just a solution of the mathematical model - and often only an approximate solution of that. It's true that I don't know the tensile / shear yield stresses that were used in the animation

Still, I read that .45acp ballistic gel peneration is still deeper than a lot of human bodies are wide -  and a chain of that will ultimately sever the two body into two parts. That's what the helicopter blade will do, too.

The "100% accurate simulation" are your wodse, not mine. But this actually does not look like serious physics simulation at all. Rather some simplified physics in Blender or other similar video generation software. Also, ..45ACP is a much smaller object that will penetrate much more easilly. And don't forget that a human body also contains bones (which also the video appears to ignore).

I do believe that the blade can cut a person in half. But these particular arguments are simply not convincing.

I agree .. "100% accurate" in Blender was for laughs, and obviously the whole animation was made for laughs. It was my geek side that felt compelled to take up that argument about the accuracy.

authors: Vladimir F Героям слава


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What kind of OS or programming language does the aviation use?
Windows XP because its the most stable system ever ?
C++ because its the most verstatile thing ever ?
Also I am not limiting this question to avionics but to
Garmin GPS/Glass cockpit
B737 Flight systems
Airbus A319 flight systems
F4E Phantom II flight systems
Bell 206 flight systems
In here, Flight systems can mean anything from basic fuel systems to autopilot systems
So which OS/Language does the aviation use ?

I hope the first line was a joke...

C++ isn't the most versatile language either.

So what is a flight system? Like anything modern and more complex than a TV remote or a pressure cooker, you are almost guaranteed to find more than one computers in there. The dash and fly-by-wire would almost certainly run on different computers with different operating systems (but fly-by-wire may also choose not to run any operation system at all) just because the use cases are so different.

XP IS THE MOST STABLE OS I EVER AND EVER USED and my used OS list 1-W95  2-Xp   3-Vista  4-W7   5-W8.1   6-W10  7-Ubuntu  8-Puppy linux

It might be the most stable you've used, but none of what you listed are stable enough (or even suitable for) avionics and safety critical systems.

Windows XP is way too bloated and error prone to use in avionics, even tif the microprocessors used in the equipment are even compatible with x86. Most equipment doesn't even run any sort of Real Time Operating System.

I Wonder what is the most stable mainstream os is...

For the OS: See this answer
btw... XP isn't the most stable system ever.
For the programming language should be any ok as long as it meets the certificate mentioned in the linked answer.

source: Stack Exchange

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sort: votes


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What is this air-scoop behind the cockpit of the Polikarpov I-153 and Stearman?
(Source)
There is a Ferrari-looking air-scoop behind the cockpit of the I-153 and most of the Stearman planes too.
What is that?

@ymb1 I wasnt (Or werent ?) thinking it would be that bad, I simply copy pasted an "English language object template" and replaced the words

-1 wrong colour for freehand circles :-)

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Is it possible to totally override the flight computer on the Airbus A320-family (in simple non-technical terms)?
As I know, in the autopilot oriented airplanes like an A321 the plane doesn't let the pilots pitch down when the plane gets an over-speed warning.
So what if the pitot-static system isn't working properly and the plane is stalling but the flight management systems doesn't let the pilots pitch down?
What will happen? Will the plane crash or is there a button on the FMC that disables all the auto management and autopilot functions so the pilots can do whatever they want in an emergency?
How does it work without being too technical so someone like me can understand?

There are more than one computers and they vote. When the vote has a tie then all computers gives in and hope the pilot could take over.

@user3528438 is there an online article that shows how they work without being too technical so someone like me can understand?

Well, voting is simple. There's simply not enough to write into an article unless being deeply technical.

First of all, I want to clear one thing. An Airbus when flown manually is like any other aircraft. It is not autopilot oriented. Only when the extremities of the aircraft envelope is hit do the protections activate. And these protections help the pilot in many situations. I would not go into the details, as it is beyond the scope of the question. But if you are interested you can go to this link:
https://www.quora.com/Do-you-believe-that-Airbuss-philosophy-of-prioritizing-the-autopilot-over-the-pilot-and-not-permitting-the-latter-to-stress-the-aircraft-in-critical-situations-jeopardizes-safety-Would-you-prefer-a-Boeing-or-Airbus/answer/Anas-Maaz-1
So, can the Airbus protections be turned off? The simple answer is, Yes. If required it can be manually turned off and the aircraft control laws degraded from normal law to alternate law.
The easiest way to do it is to turn of two ADR (Air data reference) computers. There are three of them in Airbus aircraft. Once two are off, the flight control computers no longer have enough data from various sensors (pitot tubes, static ports, AOA sensors etc) to validate the information they receive. So, they will simply downgrade the control laws. Once the two ADRs are off all protections are lost except the load factor protection, which goes out only when the aircraft downgrades further into the direct law (in A320, direct law is activated as soon as gear is down in alternate law). We do this, when we practice stall and upset recoveries in the simulator. The instructor turns off the two ADRs and the fun begins.

The red boxes mark the three ADR control switches. You can turn two of them off to downgrade to alternate law. The mistake you can do here is turning off them using the knobs. Because if you do that the IR data will also go out. Keep in mind we want to get rid of air data not inertial data. Generally, ADR 2 and ADR 3 are switched off. Source:https://www.flickriver.com/photos/medau/4890404665/
The switching off ADRs cannot be found in the aircraft FCOM or the FCTM. Nevertheless, it is little secret all Airbus pilots are aware of. When I did my type rating on the aircraft, I learnt it when our instructor shut them off to practice stalls. Airbus however, mentioned the procedure in the Airbus initial type training course guide. There was a time though when Airbus had the procedure as a temporary OEB (Operational engineering bulleting) after a Lufthansa A321 suffered a spurious high angle of attack protection activation due to two faulty AOA sensors. The pilots were only able to control the aircraft by forcing it into alternate law by switching off ADR 2 and ADR 3 which was already rejected by the computers. The OEB Airbus released, numbered OEB 48, was there in the aircraft QRH until they got new angle of attack sensor modifications.
Here is a link to the BFU report:
https://www.bfu-web.de/EN/Publications/Interim_Reports/IR2014/I1_Report_14_6X014_A321_Pamplona.pdf?__blob=publicationFile

The OEB 48. Source: https://flightacademy.info/oeb-48-abnormal-v-alpha-prot
The aircraft can also go into alternate law automatically if it detects erroneous data. For example, if two of the three ADRs give conflicting data, the computers can again no longer validate the data and simply force the aircraft into alternate law.
Then there is an abnormal attitude law. This law activates if the aircraft gets into a position where computers can no longer keep it in the envelope. Keep in mind that even though the aircraft is protected, in very tight situations things can go beyond the protections. In this case also the protections are turned off and alternate law activated which allows pilot to maneuver out of the situation. For the A320 the abnormal attitude law activates if any of the following conditions are met:

Bank angle above 125 °
Pitch attitude above 50 ° nose up or below 30 ° nose down
Speed below 60 to 90 kt (depending on the aircraft pitch attitude), or above 440 kt
Mach above 0.91
Angle of attack above 30 ° to 40 °, or below -10 °

Nice answer. Also what exactly happens if you disable the inertial reference too?

@DeltaOscarUniform You will lose almost everything. Pitch data, heading data and even the GPS so basically even the navigation. And it is irreversible in flight.

Excellent answer from someone who has "been there, done that".

@AnasMaaz "it is irreversible in flight" ? Really? Are you saying it can't be turned on again? What is supposed to happen, if someone would accidentally (or not) turn that thing off? Are you saying you'd have no more attitude indicator and you can't turn back on? I can't believe it...

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Stadium game at Miami blocking runways?
So I was looking for the Miami In in SkyVector and I saw this.
Apparently a stadium game has the power to block runways in (At least in US).
What is really going on there? I am not well acquinted with charts.

https://aviation.stackexchange.com/a/18770/43

The blanket NOTAM includes this language:

UNLESS THE AIRCRAFT OPERATOR MEETS AT LEAST ONE OF THE FOLLOWING REQUIREMENTS: A) THE AIRCRAFT OPERATION HAS BEEN AUTHORIZED BY ATC FOR OPERATIONAL OR SAFETY PURPOSES, INCLUDING AUTHORIZATION OF FLIGHTS SPECIFICALLY ARRIVING AT OR DEPARTING FROM AN AIRPORT DESIGNATED BY ATC USING STANDARD ATC PROCEDURES AND ROUTES

It is a temporary restriction, not a prohibition.  If you are departing or approaching an airport within a TFR for a sporting event, ATC will assign you a squawk that will clear you through the airspace.  I have done this several times at KBFI while games are going on.  They just don't want enroute traffic trundling through, and they ask that you do not overfly the stadiums.

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Why do pilots cut the reverse thrust below 40 km/h?
In a Microsoft Flight Simulator 2004 Boeing 747 landing tutorial, it was said to cut the reverse thrust after decelerating to 40 km/h.
What happens if that was ignored all the way to a complete stop? Would the plane start moving backwards?

You'd risk ingesting unwanted objects into the engines and in turn damge them

What are odds of that happening on an international airport (Lets say London Hearthrow) ?

Answer already available in Can reverse-thrust be used to push back from the gate?

@mins Aircraft is on the runway and decelerating, this question is a different situation.

@securitydude5 Well, in a flightsim, the risk is pretty much limited... ;-)

The question speaks of a very old 747 landing tutorial. And as such I take that to mean it would be of a 747-100/200 aircraft, and that's the reference point I'm answering from.
First, concerning the comments below the question that wonder whether you have to worry about unwanted objects on a runway at an international airport, there is no such thing as a completely clean runway, even after sweepers have just finished clearing the runway. There is always some grit—it's a matter of degree—and while ingesting it isn't going to cause immediate problems, over time it will abrade the fan blades and thus the engine performance. This may not apply to higher, body-mounted engines rather than engines mounted below the wing, at least we didn't worry about it when I was flying 727s. If our taxi speed with engines idle was getting a little fast, we would sometimes deploy the reversers of the center, S-duct engine in the tail for the taxi.
Next, why take any risk if there's little benefit to be gained. The greatest effect of reverse power is immediately after touchdown when the aircraft speed is highest. As the speed slows, reverser effect decreases rapidly.

(...) cut the reverse thrust after decelerating to 40 km/h.

40 km/h is only 22 knots. That's a taxi speed. I spent 10 years on 747-100/200 aircraft at two different carriers, and we never used powered reverse anywhere near taxi speed.
The 747-100/200 reverse levers are on the forward edge of the thrust levers. You can't raise them unless the thrust levers are in the idle position and the air-ground sensors show you on the ground. When you do raise them, they first come to a near vertical position that deploys the reversers but leaves engine power at idle. If you pull the reverse levers aft to get greater than idle reverse thrust, you're doing so against a spring loaded force such that if you relax the pressure, the engines will return to idle.

What happens if that was ignored all the way to a complete stop? Would the plane start moving backwards?

Staying in reverse down to 0 km/h is simply not done. However, let's say you did it. If you had the reversers deployed but were at idle power, I doubt the aircraft would move backwards.  Reverse thrust is not as efficient as forward thrust. Depending on the engines and how heavy you are, 747-100/200s can start to move forward at idle forward thrust, but the usual procedure is to come to "breakaway" thrust to get the aircraft moving and then go back to idle.
If you came to 0 km/h in reverse with significant engine power, then, yes, you would start to move backward. But, of course, the chief pilot would hear about it, and probably fire you.
I know of one instance where a 747 was backed up using reverse thrust to clear a runway in an extreme situation in a third world country, so it can be done.

"I know of one instance where a 747 was backed up using reverse thrust to clear a runway" Seeing how the typical 747 lacks rear view mirrors, that must have been an interesting experience for the pilots. Makes me wonder if they did something like actually open the side window of the cockpit and look out that way.

Here are some exceptions noted, especially older bigger planes with rear mounted (or higher mounted) engines. But even than it's loud and burns much fuel.

@MichaelKjörling Just as a matter of information, the side windows of the cockpit in 747-100/200 aircraft can't be opened. My guess is that's true of all 747 models. In the instance I cited, they did have a problem in that one of the main gear trucks, probably a wing truck, reportedly went off the runway edge while they were backing.

The big concern is that thrust reversers blast fan or exhaust air outwards and forward of the engine nacelle.  If there is loose debris on the ground, or on unpaved airfields, this debris is kicked up into the air around the engines.  At higher speeds, the engine intakes will remain clear of it, but at lower speeds, there is a possibility of the debris being ingested into the engines, causing damage.  This is also done when landing turboprops with the power levers in reverse to prevent debris from being kicked up into the propeller discs.


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When temperature increases what happens to the air molecules and aircraft while landing and takeoff during hot weather?
Just out of curiosity on a hot weather with  temperature increases what happens to the air molecules and aircraft during landing and takeoff?

Welcome to Aviation.SE. I'm sorry, but I think this is either a bit too broad (not to mention unclear what you really want to know). Could you please narrow the question down? As it is now it would require several books to answer, and thus it is not a good fit for this site.

When temperature increases, air becomes less dense. Lift depends on air density, in hot weather, difference is compensated by a higher speed or a higher angle of attack, or a combination, up to allowed limits. Or the crew may decide to decrease mass (less passengers, less cargo) to need less lift.

@Nick: it might be that your question is so broad because you might not really have narrowed the scope of your question down yourself. So why don't you add some bullets on what specifics you are most interested in. And from there you can start your journey.

@rul30 what i meant to say is in general what effect does air molecules have for landing and takeoff in this case.

If all else is equal, an increase in temperature will result in a decrease in density of air molecules. To fly, a wing leverages these molecules, so the aircraft will need to fly faster to generate the same lift. Therefore the takeoff and landing distances are increased.
Engine performance is also impacted. Most engines outside of NASA breathe air and so perform better when that air is dense. Jet engines also have a maximum exhaust gas temperature they can withstand, and in very hot temperatures the amount of thrust they produce needs to be lowered so as to not exceed that value. This is the basic premise of how Airbus ‘assumed temperature’ works, where the pilots tell the engine that the temperature is hotter than it actually is, so the FADEC automatically caps the thrust.


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Why is the A330/A340's alpha-floor protection disabled above mach 0.53?
One of the A330/A340's several means of flight-envelope protection is something called "alpha floor" protection.  In essence, if the aircraft's angle of attack is excessively high, TOGA thrust is automatically commanded on all engines to help ward off a stall.
There are a number of situations where alpha-floor protection is inactive, most of which are cases where automatically applying TOGA thrust would be unnecessary or would result in control difficulties.  One of these, however, is... whenever the aircraft is above mach 0.53?!

(Excerpt from A340 FCOM, highlighted by user14897 here at AvSE.)
Given that it is, in fact, possible for an aircraft to be simultaneously above mach 0.53 and in danger of stalling (especially at high altitudes, where a given mach number corresponds to a much-lower IAS - and, thus, a much-higher 1-G AoA - than it does at lower altitudes), why is alpha-floor protection disabled beyond mach 0.53?

I would be suspicious that, at higher Mach numbers, there is a risk of high power settings aggravating the problem at high AoA, which is why the design limits its implementation to regimes of the envelope with limited compressibility effects.  There is also the possibility that you may not be able to achieve angles of attack near the critical AoA w/o exceeding the flight load limits and causing structural damage.

@CarloFelicione: Structural overload would be a reason to disable alpha-floor protection above a certain IAS, not a certain mach number, and compressibility effects shouldn't be a major problem for modern jetliners with benign transonic-flight characteristics.

But high AoA at high Mach numbers can result in undesirable aerodynamic effects as well.

Try to see it this way: ALPHA FLOOR is a protection function of the AUTO THRUST SYSTEM, and it protects the aircraft from excessive speed decay. It does not primarily protect the aircraft from stalling. That can of course a possible outcome, if you don't increase thrust to accelerate.
Stall protection is primarily done by the low speed protection (high AOA protection of normal law), where the aircraft commands nose down so it does not decelerate below V_ALPHA_PROT (thus maintaining actual AOA <= ALPHA_PROT). And that protection is working above M.53.
One example for ALPHA FLOOR: you are in approach with Flaps Full, Idle Thrust (Manual Thrust) and nearing V_APP. Environmental influences (loss of headwind, increase of tailwind, gusts) or a shallow descent or even level-off could even further let your speed drop. That is where ALPHA FLOOR kicks in, because the PRIMs calculate, that you are in a low-energy state. To prevent the aircraft from automatically pitching down, the auto thrust commands TOGA. If everything goes well (as the engineers intended the protection to work), the speed decay is prevented just in time, so that the low speed protection does not need to be activated. In this case, alpha floor makes sense.
Other example: you are in cruise flight, near MAX REC ALT and near green dot speed. It does not take a lot (sudden change in wind, turbulence, excessive pitch input in manual flight (which you should not do at cruising altitude)) to let the speed drop to V_ALPHA_PROT (which is very close to green dot in this thin air near max altitude). If you are flying in alternate law (which we do in the simulator for stall training), the stall warning will activate instantly. Maybe the Auto Flight System disengages, because the speed drops below V_LS minus 5. In both cases, it would do more harm than good to have TOGA thrust, which can cause a pitch up moment, that is hard to control manually at these high altitudes. The only thing to do to save the airplane is to pitch down (nose down to unload, g-load wise), recover speed, increase thrust smoothly and recover the flight path.
These are two edge cases. And somewhere in between, there is a point where alpha floor does not make sense anymore as the best way of protecting the aircraft in all possible scenarios. And apparently, the engineers determined M.53 to be this limit.


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Why does the DC-9's antiskid system have to be manually disarmed during landing rollout following a ground-shift-mechanism malfunction on takeoff?
An aircraft's ground-shift mechanism (usually a sensor wired to the nosegear strut that looks to see whether the strut is compressed or not) tells the aircraft whether it's on the ground or in the air.  This determines how the aircraft responds to certain situations; for instance:

Many aircraft's spoilers1 can only extend to the full-up ground-spoiler position if the aircraft is in ground mode.
Applying TOGA thrust with the flaps up triggers the takeoff-warning horn in ground mode but not in air mode, whereas the stall warning, in contrast, can only sound in air mode.
Reverse thrust, on most aircraft so equipped, is generally locked out in air mode, and the minimum thrust available changes from the ground-idle setting to the considerably-higher flight-idle setting when the aircraft lifts off.
The outflow valve on most pressurised aircraft automatically goes to the full-open position when the nosegear strut compresses (this depressurises the cabin, allowing the doors to be opened when the aircraft reaches the gate).

The ground-shift mechanism can occasionally malfunction, in which case fun things can happen, like the engines refusing to reverse upon landing and the stickshakers going off during taxi (if it fails in the "air" position) or the takeoff-warning horn going off when you raise the flaps during climbout, the landing gear staying locked down, and the aircraft refusing to pressurise (if it fails in the "ground" position); the usual workaround is to force the aircraft into one or the other mode using circuit-breaker fu.
One specific type of aircraft (the DC-9) has the following interesting entry in the abnormal-procedures section of the AOM, regarding what to do during landing if the ground-shift mechanism failed upon takeoff:

Approach and landing:
If landing gear was not retracted prior to landing, ground spoilers must be operated manually.
AIRPLANE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. REPRESSURIZE (PNF)

Ensure airplane is repressurized prior to landing.

ANTI-SKID SWITCH (before 30kits ) . . . . . . . . . . . . . OFF (PNF)

During landing rollout and prior to 30 kts, momentarily release brakes and place Anti-skid switch to OFF.

GROUND CONTROL RELAY C/Bs (if pulled) (H20 and J20) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . RESET (C or FO)

Reset Ground Control Relay circuit breakers
  during taxi and verify that circuits are in the
  ground mode.

[NTSB AAR-96/07, page 134 (page 144 of the PDF file of the report); my emphasis.]

Why does a ground-shift-mechanism failure require the DC-9's antiskid system to be manually deactivated during rollout?

1: (Though not all.)

I've never heard of the term "ground shift mechanism" in 40+ years in the business.  Is that a Douglas term? They are usually called "Weight Switches" or "Squat Switches" if they are just microswitches, or Weight on Wheels, or WOW, sensors if it's a proximity sensor system.


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Why does the MCAS use the horizontal stabiliser rather than the elevators?
The Maneuvering Characteristics Augmentation System (MCAS), found, in two slightly-different variants, on the 737 MAX and KC-46, provides nose-down pitch inputs in certain very-high-angle-of-attack flight regimes to help make it easier to keep the aircraft from stalling;1 unlike ye olde stickpusher, another system used by many aircraft to prevent stalls,2 the MCAS provides these pitch inputs by moving the aircraft's horizontal stabiliser (something otherwise only done to trim the aircraft, which involves stabiliser movements of far lesser magnitude and rapidity than those produced by an MCAS activation), rather than the elevators (those things used for pitch control under essentially all circumstances that do not render them [the elevators] nonfunctional).
The elevators, however, are perfectly capable, on their own, of producing the necessary nose-down pitch input; this is evidenced by the fact that, during flight testing of the 737 MAX, when the aircraft's hitherto-unsuspected sometime pitch-up tendency was first discovered (and, thus, long before the MCAS, not developed until said tendency had become obvious, was ever dreamt up), recovery from a near-stall was still easily effected (albeit requiring slightly more effort on the pilots' parts when flying manually than it would have on a 737 Original, Classic, or NG) using the elevators alone; for that matter, recovery from even a fully-developed stall - well past the point at which the increased pitch-up tendency becomes apparent - is performed using the elevators alone.  Using the elevators rather than the horizontal stabilisers has at least three obvious benefits:

Using the elevators for automatic-stall-avoidance purposes allows the pilots to override a malfunctioning pitch-down system3a by pulling on the yoke, instead of the decidedly-non-intuitive method of letting go of the yoke (you try making yourself do that when your aircraft is trying to go kamikaze), tripping the aircraft's autotrim switches, cranking the manual-trim wheels (all necessitated by the horizontal stabilisers being larger than the elevators, and, consequently, able to produce a considerably greater maximum pitching moment than can be countered by the elevators alone4), and only then pulling back on the yoke.
Due to the aforementioned smaller (but still quite sufficient for our purposes5) size of the elevators compared to that of the horizontal stabilisers, the maximum pitch upset that can be produced by a malfunctioning pitch-down system is considerably less severe for an elevator-actuating system than for a horizontal-stabiliser-actuating system.3b
When the elevators are released, they return to their faired position, in which they produce no net pitching moment;6 in contrast, the horizontal stabiliser does not return to its previous position (it would otherwise be useless for trimming the aircraft), but, rather, has to be actively driven back to a position suitable for normal flight, leaving the aircraft out-of-trim (potentially quite severely so) until the stabiliser can be cranked back.7

Given all this, why does the MCAS use the horizontal stabilisers for its pitch inputs, rather than ye olde elevators?

1: The 737 variant also has the somewhat-less-than-optimal ability to provide said nose-down pitch inputs if the AOA vane feeding it malfunctions (the KC-46 variant eliminates this failure mode by requiring that both of the aircraft's AOA vanes indicate an above-threshold attack angle simultaneously in order for the MCAS to activate).
2: Albeit included for somewhat different reasons; aircraft with stickpushers, which are almost always T-tailed aircraft, generally need them because they otherwise can progress rapidly from the initial stall to an unrecoverable deep stall, whereas the MCAS, in contrast, was developed to counteract a pitch-up tendency which makes it slightly easier to enter a stall in the first place (the stall itself is always recoverable, even from far past the critical attack angle).
3a, 3b: This is especially important for the 737 MAX's MCAS variant, due to the aforementioned design incompetence allowing a single failed sensor to make the system go haywire.
4: The redesigned MCAS-737 version used for the 737 MAX upon return-to-flight contains a workaround for this problem, in that the MCAS will be incapable of commanding stabiliser deflections large enough to not be counterable using the aircraft's elevators, but does not address the issue of the MCAS using the horizontal stabiliser at all, rather than the elevators.
5: The only parts of the aircraft capable of generating a pitch-up moment large enough to saturate the elevators are the elevators themselves (duh) and the horizontal stabilisers (which, if they're running away uncontrollably to begin with, are somewhat unlikely to magically respond to one of the aircraft's computers telling them to do otherwise), and, if something external to the aircraft (such as a tremendously-powerful updraft) is producing a pitch-up moment of this magnitude, a) someone's already screwed up badly in order for the aircraft to be encountering something capable of doing this to it, and b) you're screwed six ways from Sunday no matter whether you're flying a 737 MAX, a MiG-29, or a Nimbus 2000.
6: Which is presumably why all stickpusher-equipped aircraft use the elevators for stall avoidance, rather than the horizontal stabilisers - to avoid leaving the aircraft out-of-trim following the stall-avoidance manoeuvre.
7: When combined with the points raised in the previous bulletpoint, this has the additional unfortunate side effect of potentially being able to produce a completely-unrecoverable-by-any-means-short-of-divine-intervention upset even with all AOA vanes fully functional, if the stabiliser and/or its drive mechanism becomes mechanically jammed in an extreme-pitch-down position during an MCAS-commanded pitch-down manoeuvre and cannot be returned to a saner angle upon the conclusion of said manoeuvre.

Way easier to certify.  The autopilot is typically a system developed by a 3rd party, like Rockwell Collins (or just Collins nowadays) and Boeing would have had to have the autopilot manufacturer, whomever it was, participate and do most of the development.  Using the stab system would allow them to conduct development totally in house.

Anonymous downvoter, work up the courage to show thy face.

MCAS is NOT about preventing stalls, and any question that works from that premise can only lead one out into the weeds. Its purpose is to affect the control feel in a certain regime. MCAS isn't there to prevent the aircraft from stalling; that's still the pilots' job. (Yes, I recognize that there are articles written by ignorant reporters which claim that MCAS is about preventing stalls; they're wrong too.)

Sorry my typed comment wasn't fast enough for you - the iPad keyboard is only so quick. I started typing the comment right after downvoting your question.

This is a perfectly valid question... Why the downvotes? 737 Mach Trim biases the column and elevators instead of hstab, so it's perfectly valid to ask the question.

I second @Ralph J’s comment. MCAS has never been never intended to avoid stalls or anything. Initially it was a fix for maneuvering stability issues. Stick force is supposed to increase as g is increasing, however for 737 max it was getting lighter at certain high speed regions. It was a good fix initially. Later in the program same stick-per-g problems have been found in some approach speed cases also. They have decided to use same MCAS computers to fix that also, however only this time they decided to use single AOA input. And now we’re here.

@Kolom: Yes, and the reason why stick lightening is a problem is that it makes it easier to unintentionally stall the airplane.

I would say it was more of a over-g concern rather than stall, initially.

45 manual trim wheel turns = 1 MCAS application has me a bit worried.  That, along with the leading edge laminar bubble forming and bursting?  Old time B-29 take-off techniques should be reviewed, as they had to be very careful when their planes were overloaded with fuel.

MCAS uses stabiliser input to retain full elevator authority in both directions for pilot input. MCAS is set up as an Inner Loop autopilot: it controls behaviour around the CoG of the aeroplane without displacing the cockpit flying controls.
For aeroplane pitch control there are indeed two options: the stabiliser and the elevator. If the elevator is chosen as the aerodynamic pitch control input, the MCAS actuator superimposes its input onto whichever column input the pilot generates - inner loop input would then be an elevator offset.
Problem with this is: the total elevator authority does not change, so if MCAS offsets the elevator in a certain direction, there is less elevator deflection available for the pilot in that same direction.
The flight control trim system is by definition designed as an offset system which retains full pilot elevator authority in both directions, and in the B737 the stabiliser acts as the pitch trim. It is therefore the logical choice for an inner loop autopilot pitch control system.
Image source
Note that in the B737, when the stabiliser deflects the elevator neutral point deflects with it.


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Why did the 707 and DC-8 continue to use the JT3D even after the JT8D became available?
Pratt & Whitney’s first-generation turbofan was the JT3D (a derivative of the company’s first-generation turbojet, the JT3C), which entered service in March 1961, and, due to its greater power and lesser noise and fuel consumption, quickly replaced the JT3C (and also P&W’s second-generation turbojet, the JT4A) on the aircraft that had previously relied on the JT3C and JT4A (two civilian [the 707 and DC-8]1 and two military [the B-52 and KC-135]).2
However, the JT3D, although a vast improvement over the loud, inefficient turbojets it replaced, was still very much a first-generation design, with problems not seen on newer turbofans, and still quite the screamer and kerosene-guzzler even by the standards of just two years eleven months later, when Pratt & Whitney came out with their second-generation turbofan, the JT8D (entered service February 1964 with the 727).  The JT8D was a vast step ahead of the JT3D, and is still practically the state of the art for civilian low-bypass turbofans;3 not coincidentally, it is also the best-selling low-bypass turbofan ever, and the second-best-selling jet engine of any kind in history.4
Yet, even as Boeing and (McDonnell) Douglas readily adopted the newer, better-designed, quieter, more efficient JT8D for their second-generation jetliners (the 727, DC-9-10-through-50,5 and 737-100/-200), they continued to use the old JT3D on their first-generation jetliners for as long as those aircraft remained in production; JT3D-powered DC-8s continued to spawn in Long Beach until 1972, and the guys and gals from Washington State kept on putting JT3Ds on new 707s all the way up until 1979.  Admittedly, the early models of the JT8D had somewhat less thrust than the JT3D, but they could easily have been upbeefed to JT3D-equivalent power levels - as was, indeed, done in the 1970s to create the JT8D-200!
Why did Boeing and (McDonnell) Douglas continue to use an old, outdated engine for the 707 and DC-8, even after the JT8D came along?

1: Technically, not all pre-JT3D 707s and DC-8s used a P&W turbojet (the 707-420 and DC-8-40 both used the Rolls-Royce Conway, the first turbofan ever to fly), but the vast majority did (as U.S. airlines were reluctant to buy airliners with foreign-made engines, meaning that most orders of Conway-equipped 707s and DC-8s were for the smaller European and Canadian markets).
2: The turbojet variants of these aircraft were the 707-120, DC-8-10, B-52A-G, and KC-135A (JT3C) and the 707-220/-320 and DC-8-20/-30 (JT4A); the JT3D powered the later 707-120B/-320B/-320C, DC-8-50/-60, B-52H, and KC-135E.
3: Not that that’s saying much, given that the market for civilian low-bypass turbofans has (with one notable exception) been essentially extinct since the first narrowbody-sized high-bypass turbofans broke into the market in the early 1980s.
4: ...behind only the engine that finally evicted the JT8D from its niche, the General Electric/SNECMA CFM56 high-bypass turbofan.
5: Along with the DC-9-80, when it came along (which happened, ironically, shortly before the JT8D was rendered obsolete by GE’s French connection).

When retrofitted with JT3D, KC135E is 14% more fuel efficient than KC135A. Considering the users of late production 707s are mostly military, this 14% fuel efficiency improvement might not be as attractive as you think, compared with other non-performance reasons to use old engines (i.e. support infrastructure)


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Is the transition altitude around Denali still 18 kft AMSL, and, if so, how is this handled?
In North America, the transition altitude - the altitude below which everyone reports their altitude in feet above mean sea level (AMSL) and sets their altimeter to whatever the weather dictates that the local altimeter setting be, and above which everyone reports their altitude as a flight level (FL)1 and sets their altimeter to 29.93 inches of mercury (inHg) - is 18 kilofeet AMSL, this altitude having been chosen so as to put the transition altitude well above the elevation of every airport on the continent.
However, although the highest airports in North America are well below 18 kft, the highest land in the continent is not; Denali, the highest mountain in North America, reaches up all the way to 20.31 kft AMSL.  It’s also not particularly inaccessible, and happens to sit in one of the most aviation-centric - indeed, in great measure, aviation-dependent - regions of North America, fairly close to said region’s major city and said city’s major airport.
Given that one’s ability to maintain terrain clearance (read “avoid flying into the side of the mountain”) depends on one’s height above the ground, which depends on one’s actual altitude, on the ground’s actual altitude, and on the difference between the two,2 how is the situation of a mountain poking its nose above transition altitude handled?  Is there a higher-transition-altitude bubble surrounding Denali?  Are pilots required to set one baroaltimeter to 29.93 inHg (for flight-level purposes) and a second baroaltimeter to the local altimeter setting (for terrain-clearance purposes)?  Do they simply have to watch their radar altimeters like hawks anytime they’re flying near Denali’s peak?  Something else?

1: One flight level is roughly equal to one hectofoot; it does not equal exactly one hectofoot unless the sea-level barometric pressure happens to be 29.93 inHg and the atmospheric profile happens to match the International Standard Atmosphere (ISA).
2: And given that, while terrain clearance is always a high priority, it’s even more so where even the gentlest crash would be unsurvivable for anyone but a well-acclimated mountaineer, due to Denali being inconsiderate enough to locate its peak in what is, for non-acclimated persons, the Death Zone.

I understand the question but I'm not sure what the problem is? VFR flights see and avoid Denali; IFR flights are either above it or planned/vectored around it. Of course things don't always work out as they should and I have zero experience in Alaska, but I can't immediately see why the risk of CFIT on Denali would justify special rules compared to the many other places where CFIT is a risk.

The nearest airway is almost 30 mi away T242, and the minimum sector altitudes are 22700 in the area of Mckinley. But normally the minimum sector alts are ASL, and I would assume they are in this case, and looking at it from a strict technical standpoint where you were observing the sector minimum IFR alt, say wandering around with no comms, I would think you would observe the min IFR alt in the sector as ASL based on the Fairbanks altimeter setting, not a flight level.  This is actually an interesting question.

@Sean I would look into how that is handled in Europe where the transition altitudes are very low and all sorts of terrain intrudes into the flight levels.

This is really a non-issue. Above FL180 you have to file IFR and be in contact with ATC, and if for some reason you are flying away from the airway and towards the mountain, you would be contacted to correct and/or vectored away from the rock.

@JohnK, in Europe the transition altitude varies by sector, and is low only in sectors that don't have any high ground. So I don't think that much high ground intrudes into the flight levels—though I didn't look up the sectors with high ground to check, so I might be wrong.

@JuanJimenez Yes in practical terms I agree, but there is still the need to address the technical issue that Sean has raised.  There is a minimum sector altitude published on the IFR chart for that area that is over 22000 feet.  Is that published sector altitude QNH (ASL based on local altimeter) or QNE (a flight level)?

@JohnK I don't see a link for any IFR chart in the question...

@JuanJimenez Try this... https://skyvector.com/   If that link doesn't take you to a chart where the area is question is centered in the view, hunt around for the IFR enroute chart for southern Alaska that includes Anchorage/Fairbanks on Skyvector.

@JuanJimenez Class A airspace does not exist below 1500 AGL, and therefore there is no requirement to be IFR and on a clearance when, say, sightseeing around Denali, even when above 18,000.

The FAA and National Park Service publish a booklet on flying around Denali, available at https://www.nps.gov/dena/planyourvisit/upload/Reporting-points-FAA-Brochure_2014.pdf . It does not talk about altimeter settings, except to say to make sure it is set accurately. It does include info on reporting points and common traffic advisory frequencies. Most aircraft will be below 18,000 MSL most of the time and on QNH, so in the absence of other local info, I wouldn't set it to anything else. I would call and get local advice and info from one of the tour ops before actually flying here.

@Dave-CFII Do you have a source for that statement? The AIM makes no such distinction. It only says Class A starts at FL180 MSL.

Aha, found it in 14CFR.
3-2-2. Class A Airspace
§ 71.33 Class A airspace areas.
(b) That airspace of the State of Alaska, including that airspace overlying the waters within 12 nautical miles of the coast, from 18,000 feet MSL to and including FL600 but not including the airspace less than 1,500 feet above the surface of the earth and the Alaska Peninsula west of longitude 160°00'00" West.

Guys my basic question still stands; is the sector alt in the IFR enroute chart, of 22700 ft, QNH or QNE?  I would assume QNH if I has to choose.

@JohnK according to the Aeronautical Chart User's Guide, "The Off Route Obstruction Clearance Altitude (OROCA) is depicted on IFR Enroute Low Altitude and Pacific charts and is represented in thousands and hundreds of feet above MSL." It's an elevation figure, which means you would measure it with QNH. QNE would make no sense (the chart makers didn't know what the atmospheric pressure is today when they printed the chart).

Sean I guess you could actually break the answer into two parts; how is it handled in a normal operational way, and how it is handled from the standpoint of an extreme theoretical emergency situation, where find yourself, somehow, in that airspace with nothing but the minimum sector altitude on the chart as your guarantee of obstacle clearance (IFR rules are all about separation of aircraft and obstacle clearance, in the end).
Say you were IFR, in cloud, and had a total comm failure and were lost and thought you might be near McKinley and therefore needed to observe the sector altitude of the airspace around it, 22700, ft as your last gasp guarantee you won't hit the mountain (that's really what the sector altitude is for).  Even though you are in the flight levels, you would need to set your altimeter to the closest local altimeter setting you could obtain.  In the IFR world, the rules are the rules, but still, when it comes down to survival, ya do what ya gotta do, applying common sense.
That's the way-out-there theoretical worst case, where the fact that the min IFR ASL altitude is above the transition level has to be allowed for by the crew to save their skins.
Another, maybe slightly more likely, theoretical case:  Say ATC has you on a heading that will take you across Denali at FL280.  You have a comm failure before that.  Well, no big deal, carry on as cleared following IFR comm failure protocol. Then right when you are in the 22700 ft sector, you have a depressurization and have to initiate a descent to the minimum IFR altitude right now.
That 22700 ASL sector alt is as low as you can go until you are clear of that sector and can get down to 10000ft.  You'd just have to use common sense based on the circumstances in the moment, and you'd set the best alt setting data you had, plus temperature correction, and maybe some extra fudge factor for comfort, to come up with an interim level off altitude until you were clear of that sector.
In the normal operational world, you just go where ATC tells you and how high ATC tells you.  If you are on the nearest airway, that's nearly 30 miles east, so no big deal.  If you being routed by ATC over the mountain, ATC takes care of the altitude assignment and makes allowance in the flight level assigned.  In any case, I would bet that ATC generally does not route aircraft over those sectors to avoid emergency descent issues as described above.

14 CFR 71.33(b) defines class A airspace as...
(b) That airspace of the State of Alaska, including that airspace overlying the waters within 12 nautical miles of the coast, from 18,000 feet MSL to and including FL600 but not including the airspace less than 1,500 feet above the surface of the earth and the Alaska Peninsula west of longitude 160°00′00″ West.
So for Denali you've got a 1,500 ft buffer zone where it's not class A, but you'd better have oxygen and hope you don't run into mountain waves or other strange things that could make you go  against the mountain side, or climb like a lovesick ghost into altitudes you don't want to be. :)

That does not say anything about the transition, and Class A and transition altitude, while coincident in most USA, are unrelated concepts.


text:
Is this just a generic B737 or does it have a specific name?

Is this just a generic B737 or does it have a specific name?


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Is this a 737-800 or 737 MAX 8?

Is this a 737-800 or 737 MAX 8?

The tail number in the photo looks to be A6-FEA, which is a 737-800. (The A6-F part is harder to make out, but it's used by flydubai's entire fleet.)
I would suggest using the highest resolution photo available and zooming in, as your aircraft ID questions all seem to have visible tail numbers, though some are hard to make out once they've been scaled by the Stack Exchange uploader.


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What is this high-wing jet airplane?

Can someone help me in identifying this plane?

It's probably a Bae 146-200 / Avro RJ
Here is the Wikipedia article.
If you want to know if it's really a -200 you could try and count windows or measure relative lengths.


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How close can supersonic airplanes get to subsonic fuel efficiencies?
I was struck by this sentence in @therac's excellent answer for why quieter supersonic planes don't offer efficiency gains.

Supersonic L/D will always be lower than subsonic, like a best-case of 7:1 vs 20:1. So it will always consume a lot more fuel and cost more.

Are there efficiency gains with quiet supersonic technology?
It made me wonder how much of the higher drag is made up by traveling at a higher speed? For example if drag is three times higher at three times the velocity, overall fuel consumption should be similar burning fuel at three times the rate for a trip that only takes one third as long.
So my main question is, how big is this effect and how close has any supersonic plane ever got to subsonic fuel efficiency while flying supersonic? Specifically what triggered this question is I wonder how the B-70 Valkyrie achieved such a relatively long range despite its extremely high cruising speed.

You are partially right - if thrust-specific fuel consumption (TSFC) was the same, a L:D of 7 at average Mach 2.0 would bring the same burn per mile as a L:D of 20 at Mach 0.7.
The tie-breaker is that TSFC is generally higher for supersonic-capable engines, and for these engines, is again higher at supersonic speed than at subsonic. The Concorde's engines have been addressed in detail.
Even being relatively efficient, they consumed ~2x the fuel per pound thrust compared to a subsonic turbofan at subsonic speed.
So there's two things making supersonic fuel economy worse:

Lower L/D
Higher TSFC

Versus one making it better - higher speed.
Overall, for Concorde vs conventional airliner, you get 3x worse L/D, 2x worse TSFC, but 2.5x higher speed, resulting in ~6/2.5 ~= 2.4x worse fuel burn per ton-mile. Thus, fuel economy still favors subsonic aircraft.

How close can supersonic airplanes get to subsonic fuel efficiencies?

Depends on how you define efficiency. If you mean transporting the same people from point A to point B then the answer is simply: not even remotely close.
Flying supersonic has mainly two big disadvantages in respect to flying subsonic:

the need of a stronger airframe to deal with the high skin temperatures which soften the structure; and
the need of a very big delta wing in order to minimise wave drag.

Even just for these simple reasons, a supersonic airframe is going to be heavier (and therefore less efficient) than an equivalent subsonic design. And once we add wave drag to the picture, the game for the supersonic airplane is irremediably lost. Just for a quick and dirty comparison:

Concorde could carry 120 passengers for 7,200 km (4,400 mi) burning 95,000kg (211,000lb) kerosene (which took up more than 50% of its MTOW); her empty weight was 78,700kg (173,504 lb);
An Airbus A319 can carry a bit more passengers on more or less the same range burning only 24,000kg (53,000lb) kerosene (some 30% of its MTOW); its empty weight is 40,800kg (90,000 lb)

The ratio of their empty weights is around 0.5 while the ratio of their fuel consumption is 0.25: that means that a supersonic airplane must carry around twice as much airframe than an equivalent subsonic design, burning four times as much fuel. These ratios are simply unbeatable.

I wonder how the B-70 Valkyrie achieved such a relatively long range

No wonder rather a lot of kerosene: 60% of the MTOW to be precise, i.e.
140,000kg out of 245,000kg.

Perhaps that's why they tried to bring straight wings through the sound barrier in 1947.

No. The power consumed by drag is equal to the drag force times the velocity. At three times the speed and three times the drag, the airplane will consume fuel at nine times the rate.

For jet aircraft, the fuel low (pounds per hour) is generally considered to be proportional to the thrust -- not the power.
So if L/D is 1/3, then 3x the drag is true -- but, you cover ground 3x as fast, so you burn that fuel for 1/3 the time.  Those two cancel out.
However, you aren't going to cruise at Mach 3 at the same TSFC as you would subsonically, so your big penalty is there.

@Rob that’s generally true for a specific engine, but those designed for higher speed flight necessarily have higher exhaust velocity and so are more or less doomed to be less efficient at any speed.

@RobMcDonald You can't beat physics. Going three times faster with three times the drag takes 9 times the mechanical power. You can't get more power out than the energy of the fuel you put in. Turbojet engines mask this by being tremendously inefficient at low speeds, not by magically producing more energy for the same amount of fuel without limit.

@Frog -- yes, the difference in efficiency of higher speed engines is captured in the  change in the TSFC -- thrust specific fuel consumption -- lbm/lbf/hr

@Chris I'm well aware of the physics.  You also can't handwave it when it needs to be written down.  Look at the standard Range equation $R=(V/TSFC)(L/D) ln(Wi/Wf)$.  3x the velocity cancels with 1/3 the L/D.  The difference for these kinds of systems is in the TSFC.  Strange as it seems, the efficiency of converting the heating value of fuel to propulsive power increases with Mach number.

Because ram air drives the compressor more and more.

@RobMcDonald You tacitly assume TSFC is not a function of the airspeed it is meant to operate at. You can't slap a jet engine designed to operate at mach .9 on an aircraft going mach 2.7 and expect it will still work, much less produce the same thrust for the same amount of fuel.

@Chris I certainly do not.  I explicitly state that the variation we see is due to variations of TSFC.  If we were to re-derive the range equation in terms of power specific fuel consumption PSFC, then the velocity would drop from the equation and you would only see the L/D penalty.  However, PSFC is not as useful for jet-thrust kinds of engines as it varies substantially more.  TSFC is relatively constant over a reasonable operating range for a given engine type -- I agree that it is very different say between a HBPR TFan and a Scramjet.

In the drag equation, speed appears with a $^2$ so that the power dissipated due to drag goes with the $^3$ of the speed: at three times the speed, power due to drag is going to be 27 times higher, not 9.


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What is the difference between a VOR and a VORTAC?
Confused about the difference between a VOR and a VORTAC?

Welcome to aviation.SE! Your question has already been asked here, with more details here


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Could a FOSS autopilot system ever pass FAA regulations?
Think something like ardupilot but for manned aircraft.

I doubt it, it could possibly be used in Experimentals, but there are manufacturing, quality control, and testing requirements that would be difficult or impossible to manage with public contributions.

Closely related. In particular, this answer might help you. I don't think we can really say if it will "ever" happen, because that's speculation and we don't know how/if the rules will change in future.

Since FAA does not force the source code to be confidential, so the owner of the code has full freedom to license it to whoever under whatever license. So while hobbyists developing such systems from scratch is hard, vendors developing it in house and open it to the public is highly possible. In fact I would say most of the contributions to FOSS are funded by vendors not volunteers.

Short answer: technically and legally yes, a free open source autopilot could be certified.  But I think it is unlikely to happen anytime soon.
Long answer: Aircraft software certification is governed by DO-178C. There is nothing in there that says anything about whether the source is open vs closed, or free vs non-free.  What it does lay down is a lot of very rigorous requirements for proving that the software does what it says it is going to do.
For example, for something like an autopilot, an independent testing/validation would typically be required.  That means the person who writes/codes the software and the person who tests the software have to be different people. i.e. you must have a fresh set of eyes looking at it. Further that testing will have be very extensive, covering every possible scenario your autopilot could encounter.  You might have to mock up an entire fake airplane, with simulated sensors and simulated actuators, and feed the autopilot simulated data and see if the actuators move like they are supposed to.
You also need to provide a massive amount of very careful documentation about all parts of your software process.  E.g. the software requirements need to documented, and then you need to be able to show every step of the way on how each specific requirement gets translated into the final machine code.
An free open source project certainly could meet all of these requirements. However, they end up being very time consuming and expensive. You need an army of software engineers working all day every day for years to meet some of these requirements.  FOSS project typically do not have the level of manpower that is required to meet these requirements.

As a software certification engineer, this is a very good answer. The trick with most FOSS is that there are not documented requirements that trace to design or test. It's impossible to show that a piece of software works correctly and has no untested code if the requirements aren't there to verify the code against.

There is no practical way for Free Open Source Software to be used in any FAA certified equipment. This approach to software development encourages users to modify and contribute code, so as to benefit the entire community. Much of the motivation is to see the code improved and put into use.
FAA certification requires such extensive testing and documentation that revisions do not occur except to correct a serious flaw, and this usually means removing the hardware and returning it to the manufacturer. New functionality might require a new generation product. It is not likely that a five or ten year wait for new features would be attractive to FOSS developers.


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How does EEC/FADEC recognize/anticipate engine acceleration/deceleration?
So I'm wondering, when the engine runs at idle and the pilot sets a higher thrust level, what exactly happens, that the EEC/FADEC recognizes, that I want to accelerate? My professor said, it's anticipating the upcoming acceleration through:

$TRA > TRA_{threshold}$
$pt_3 < pt_{3_{min}}$ (cabin bleed)
$N2/\sqrt\theta < N2/\sqrt\theta_{idle}$ with $\theta = Tt2/T_{t ref}$

I get that the TRA (throttle lever angle) is higher than my previous one, hence I just raised it. But why exactly would pt_3 be lower than pt3_min, and why is $N2/\sqrt\theta$ smaller than idle? That would indicate that Tt2 has increased.

You probably need to go ask your professor for clarification.  But let's look at it this way: what would it mean if $Pt3 > Pt3_{min}$ and $N2/\sqrt{\theta}>N2/\sqrt{\theta}_{idle}$. It means that the engine is probably NOT at idle. So in that situation, if you move the throttle, you probably do want to increase thrust, but not from idle.  The EEC may have different control schedules for idle vs above idle operation.


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Are overhead bins airtight?
This question is prompted by a recent news about a dog dying while transported in the cabin overhead bin for about 3.5 hours.
Are those bins airtight enough to cause death of a (relatively) small animal by asphyxiation? According to some pics on the internet, the dog in question was a French bulldog or similar.

No, the bins are not air-tight.  However, combining the lower-oxygen levels (around 8,000 ft. pressure) with a brachycephalic animal in a dark, confined, noisy space, its easy to see how it could've worked itself into a panic and likely had a heart attack.

I'm not saying the story implies suffocation, I'm just trying to understand what might have caused the poor pooch's demise.

Any number of things could have led to the death of the dog, most unrelated to suffocation... the one possible reason that gets all the news is the one that the airline can be sued over. Let's face it - everyone likes reading bad news about airlines, which means the newsies tend to hypothesize in that direction, because it gets them more ad views.


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Why local(section) lift coefficient(CLL) is higher near the wing tips compared to the root on untwisted tapered wings and untwisted swept(aft) wings?
Why local(section) lift coefficient(CLL) is higher near the wing tips compared to the root on untwisted tapered wings and untwisted swept(aft) wings?
I know that in an elliptical wing(untwisted) the absolute angle of attack is the same in all the wing span so, the reduction in lift is 'proportional' to the reduction in area/chord of the section and then the CLL is equal in all the wing span.
I also know that in a retangular wing(untwisted), the effective angle of attack(due to the tip vortex) causes a reduction in the CLL in the tips compared to the wing root.
Even that I understand the flow pattern over swept wings(Attachment line/Spanwise airflow and it's effects on lift and in the boundary layer, adverse pressure gradient and tip stall)I just can't figure out, intuitively, the relation between this flow pattern and the increase in the CLL in the direction of the wing tips.
[ CL = L / S.q ]  Seems to be too simplistic to analise this particular case.

For the swept wing, as you go out along the wing, each section of the wing is effectively flying in the upwash of the tip vortex of the section immediately next to, and inboard of it. So, each section has its angle of attack increased by all of the sections inboard of it. The root section, of course, does not have anything inboard of it, and the tip section is affected (to at least some extent) by all the sections inboard (and ahead) of it.
Birds fly in V-formations to take advantage of this effect. Each bird is flying in the upwash of the tip vortex of the bird ahead and toward the center of the V, and is thus "flying downhill" aerodynamically.
But, that upwash increases the angle of attack, and the effects add up as you move outboard, until they reach a peak effect near the tip.
You can really see this on hang glider wings: if you stand next to one as it's about to take off, you can see the tips appear to be at a negative incidence relative to the wind, and yet they are lifting, because the wing sweep increases their local AoA.

Section lift coefficient depends on angle of attack. A greater angle of attack means higher lift coefficient.

A wing producing lift "pushes" air from below around the front and over the top. This is called circulation. When the leading edge is swept, whether from taper or wing sweep, some of that air is "pushed" toward the tip and then over the top. This happens all along the wing, so that when you get all the way to the tip there is a lot of more air going over the top than there was in the center of the wing. Think of it like this snowplow with an angled blade:

The additional airflow going over the wing the farther out you get increases local angle of attack and therefore the local section lift coefficient.

It’s because, on a tapered or a swept wing, the tips are so small that they cannot hold the vortices that are being formed, because of which the vortices are formed inboard. Therefore there is no reduction in the effective angle of attack at the tips whereas there is a reduction in the effective angle of attack inboards and hence, the local lift coefficient is higher closer to the tips as compared to the root.


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Do I need 35 hours of ground school for knowledge test for PPL?
New US student here. I'm starting part 141 flight training soon for my private pilot license, but for now prepping for the knowledge test. I am going with self-study and had a question about endorsement for the written exam.
Is the endorsement I get from the ASA Prepware tool sufficient for taking the knowledge test?

Complete two practice tests with scores of 80% or better, and request your test sign-off (endorsement) from ASA

I am confused because I've been under the impression that part 141 mandates 35 hours of ground school for taking the knowledge test (also 35 hours of flight time).
https://www.ecfr.gov/cgi-bin/text-idx?SID=2d180e467a3b85b2e34ce695dea3d322&mc=true&node=pt14.3.141&rgn=div5#sp14.3.141.f

Appendix B to Part 141—Private Pilot Certification Course
(a) Each approved course must include at least the following ground training on the aeronautical knowledge areas listed in paragraph (b) of this section, appropriate to the aircraft category and class rating:
(1) 35 hours of training if the course is for an airplane, rotorcraft, or powered-lift category rating.

If not, I might just do Sporty's ground school ($200) and get my endorsement that way.
Thanks

Why 141, if I may ask?

I don't know much about part 141 but I suggest you check their syllabus and requirements before doing anything. A part 141 school can have "examining authority", which means that they test and approve their own students and you don't need to do the regular FAA knowledge and practical tests at all. Make sure you really understand how the school's program works before you spend any money on anything. They should be able to explain that to you easily.

For 141 you need a graduation certificate to take the test. For part 61 you need an instructor endorsement. 141 is for complete courses start to end. 61 is for getting a piece here and a piece there mix and match style. in either case there is a minimum amount of ground training required before you can get your private certificate.
Any either case you don't need the knowledge test to start flying, you only need the knowledge test before your final FAA check ride.


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What kind of microphones does aviation use?
Do they use the dynamic ones or cheap ribbon ones? Also why are these microphones so small?
I guess they dont use condensers. (I am yet to see an 3.5mm jack (which is used both on the C172 and the B747) that can supply 48V phantom power to the one of those)

"Cheap ribbon ones?" The cheapest ribbon mics nowadays are $500+. They're specialty studio microphones and they're big heavy things. They're also very delicate, so they would be no good for a headset mic. Can't get much cheaper than an electret condenser and they're practically indestructible.

Microphones used in aviation are usually electret condenser microphones that do not require any phantom power (obviously there are different types as well).
While General Aviation Aircraft and many airliners use the dual PJ connectors (PJ-055 for headphones + PJ-068 for microphone), the Airbus and ATR aircraft (and probably some others) use XLR connectors. Most helicopters use the combined U-174 connector for both headphones and microphone.

What is the voice quality difference between the XLR ones used by Airbus and the regular ones used by the rest?

Audio quality usually isn't a concern when selecting a connector type. In terms of quality the microphone and electronics are more important, but in the end an aircraft is not the opera so it doesn't matter too much. XLR has the advantage of being able to provide power if needed while the PJ connectors do not as far as I know. Audio quality on the radio communications is limited by the bandwith available for the radio channel which is very limited.

When I bought my Dave Clarks in 1976 they were still offering a carbon mic and the option was the dynamic mic.  The carbon mic made you sound like you were talking from inside a trash can with the mic right in your mouth, so dynamic it was.  Electrets were just coming out and that option was quite expensive.  You can tell the dynamic mic on a DC because of the amp circuit for it which makes the housing quite large.  I can't tell any difference between sound quality between dynamic and electret.


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How do carbureted and fuel injected engines compare in high altitude?
I couldn't find enough information on the internet for this topic. What I found can be paraphrased as:

Carburetor means easy engine start while fuel injected means manual fuel start up and carburetors are cheaper.

So how do carbureted planes compare against the fuel injected ones for GA purposes especially in long distance cold high altitude flights?
I looked for the M-9 Series and the specs doesn't reveal much.

What 3 planes?  Injected engines can have better fuel flow per cylinder by ensuring the injectors have even flow, making lean of peak operation easier to achieve.  I can't get there in my carburated engine, runs rough before all cylinders can get to lean of peak. There is no intake maniold adjustments to be made.

By in particular I especailly meant the M9 series. Thanks for the comments answer too!

Disadvantages of fuel injection:
You need to do a business case.  It's possibly not worth the price.  The Bendix fuel injection system used on the Lyc is a fairly crude (by car standards) mechanical constant flow system, and the specific fuel consumption is perhaps 5-10% lower, maybe, at best, .4 lb/hp/hr vs .44 or so for a carb (cars are in the high .3s, diesels in the low .3s).  Lets be generous and say the fuel burn is 9 gal/hr instead of 10. At 100 hrs a year that's a $500-550 saving.  If you spend 5000 extra for the injected engine, it's 10 years just to break even.  Hopefully the fuel injected option is a lot cheaper than that, or you do enough flying to recoup the extra price much faster.
You prime by pressurizing the system with the fuel pump (using the mixture) to inject fuel pretty much where the primer would be on a carbureted engine; so far so good, but it's a somewhat more finicky procedure and easy to flood.
There's a little bit of a pucker factor issue because you have a high pressure fuel distribution system snaking around the engine (yes there are primer lines on a carb engine but they aren't pressurized) so there is a higher fire risk due to a fuel leak (it's the main reason carbureted engines are always updraft - nobody puts the carb on top).
When the engine is hot and sitting on hot day, you can get vapor lock in the distribution manifold and lines, sizzling away like a pan of bacon in the plenum of the cowling, making the engine really hard to start.  If you're on floats drifting away from a dock after pushing off and frantically trying to start the dang thing before you drift into the rocks, it becomes a big deal.
My personal opinion is the fuel burn reduction is not worth the costs, extra failure modes, and loss of simplicity and I prefer carburetors, for simple, low speed airplanes at least.

+1 What has not been said yet is that with fuel injectors you can safely run lean of peak while with carburetors you need to run rich of peak but like you said is it worth the additional cost.

One of the disadvantages of carbs for cars is the difficulty of finding settings which work well for a broad range of engine speeds; people want smooth idle and quick acceleration even at high rpm, and those are tradeoffs. Aero engines can be tuned for good operation at a narrower range of rpm's, and don't spend much time idling at red lights. So one of the big drivers for injection just doesn't apply to aero applications.

Agreed.  Carbureted cars suck.  But for airplanes, where they work well enough to do the job, they offer trouble-free simplicity.  Some homebuilders advocate adapting car EFI system for airplanes, but it requires a full dual channel architecture due to the ability to electronics to fail without warning.

Carbureted engines make use of a carburetor to mix fuel and intake air prior to administrating the airflow to the engine intake manifold.  Fuel injected engines make use of a fuel metering unit which directly injects fuel into each cylinder of the engine.
Advantages to carbureted engines:

Simpler
Easier to start than fuel injected engines, especially when hot.

Disadvantages of carbureted engines:

Carburetors use Bernoulli principle to draw fuel into Venturi, resulting in a temperature drop, which can result in carburetor icing.
Less uniform control of fuel air mixture entering cylinders.

Nitpicking here, but the majority of the temperature drop that causes carb ice is from fuel evaporation in the area of the butterfly.  The only reason injected engines don't need heated air is the fuel is injected at the cylinder.

Performance wise, both types perform similarly at high altitude.  Without turbocharging/turbonormalizing, neither will have enough air at altitude to create the same horsepower they can make at low altitude.  Basic chemistry/physics there.


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Why does the F-4's rear seat have a weather scope eyepiece?
In the front seat. The pilot has a flat screen radar scope that shows both the planes and the weather.
But on the rear seat. The weather scope has an giant eyepiece. Perhaps glare protection?

(angelfire.com)

That's not an eyepiece, it's a glare shield. The angle of the display made it susceptible to glare from light entering the cockpit. The shield made it easier to see, at night as well. My theory is that they got the idea from Star Trek. Spock had one too on his workstation on the Enterprise.

I don’t know if Mr. Spock will consider “Emojis” fascinating. But I hope Kirk will fight them!

Kirk would never fight emojis, he would seduce them.

Maybe an F-4 backseater can tell us how they kept from puking their guts out as they looked through the glareshield while the aircraft was maneuvering. That had to be a totally gut-snarking thing to do.

It was for glare but it was also a nice cushion for my face to smack into when an FNG pilot unexpectedly g’d up the jet while I was in the radar.


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Do any other nations have an equivalent of the "Air Force One" call sign?

Air Force One is the official air traffic control call sign for a United States Air Force aircraft carrying the President of the United States. - Wikipedia

Do any other nations have an equivalent call sign for an aircraft carrying their head of state?

I think many countries do, but most probably treat it as a military secret for obvious reasons.

It is all in your link (in the "See Also"), E.g.:

Brazil: https://en.wikipedia.org/wiki/Brazilian_Air_Force_One
France: https://en.wikipedia.org/wiki/Cotam_001
India: https://en.wikipedia.org/wiki/Air_India_One
Japan: https://en.wikipedia.org/wiki/Japanese_Air_Force_One
Vatican: "Shepherd One", or just in Italy "Volo Papale #" (https://en.wikipedia.org/wiki/Air_transports_of_heads_of_state_and_government)

Note: Often it is better to disguise who the airplane is transporting (especially when flying above a lot of different countries), and often the president has not so much power ("nuclear football"), so a hired jet it is enough, no need to communicate home.


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For the 737 Combi, How did changing the proportions of the passenger vs cargo areas work?
I am very interested in the 737 combi models and want to learn more about how they worked in practice. For the 737 Combi, How did changing the proportions of the passenger vs cargo areas work?

I have read that regulations require passenger areas to be maintained
at higher pressures than cargo areas in order to prevent potential
fumes from reaching the passengers- is that true? If so, how does
that work in terms of the air pack design and other aspects of the cabin air design?
Could operators change
back and forth the proportion of floorspace that they dedicated to
cargo vs passengers, or was it semi-permanently fixed? If it could be
changed in normal operations, about how long did it take or how many
man hours?
Could the bulkhead between the passenger and cargo areas
be located at any point inside the aircraft ("infinitely variable
bulkhead location" you might say) or were there a certain number of
fixed points that the bulkhead could be positioned?
For 737 combis
operated in a 100% passenger configuration, what did the cabin look
like next to the door? Was the cargo door basically fully finished as
though it was any other part of the cabin, or was it more industrial
looking/louder/colder?

The Boeing 737QC (Quick Change) is a Boeing 737-200 which featured a 134 in × 87 in (340 cm × 221 cm) freight door just behind the cockpit. The floor was strengthened and allowed for palletized seating for faster configuration changes between cargo and passenger flights. A switch using a system designed by Falcon Aviation in Sweden allowed the seats to be removed in 20 minutes. Each seat row would roll forward to the cargo door, then slide out into a container for storage. The container would be rolled away and cargo loaded into the space where the seats used to occupy.
The video below shows how the conversion system created by Falcon worked.

Good luck creating a toy hauler.

Great video! Very cool to see how the floor finish is integrated as a single unit with both sets of seats and the aisle. This still only addressed the example of switching from 100% pax to 100% cargo so I still am left wondering about the combined configuration and how the bulkhead is mounted and any configurations that have to be done to address air pressure or whatever other concerns of carrying cargo in the same cabin as passengers. "Good luck creating a toy hauler" exactly, this thing is basically an airliner sized Pilatus, which is so cool. The -200 was even available with a gravel kit.

For the -200QC model, there appears to be variable cargo and passenger volumes: https://www.flickr.com/photos/57440551@N03/34619249303
The "Combi" is fixed at half cargo, half passengers, and it appears to not be an original type, but a conversion after delivery.
Regarding the last point, the Cargo Door appears to have the same windows and has overhead bins.

so there appears to be minimal distinction between the cargo door and the rest of the cabin.

I definitely have seen pictures of combi models where the pax windows stop midway through the fuselage, stopping even before the cargo door, so I know that there must be some options for how you configured these. I also know that historically, some airlines purchased new Combis with cargo doors fully intending to use them for 100% passenger service, and only equipping the cargo doors in anticipation of resale market value. I wonder if those planes even retained the ability to open their cargo door. Still hoping to learn more about how these QCs work.

Alaska airlines had a couple of the true combi type (half windows) but i think they retired them 20 years ago. They actually do use the cargo space for cargo on the smaller northern routes. The also had a few with a gravel runway option, to keep rocks out of the engines. This work is actually what the 737 was originally intended for, and why it has short landing gear-> loading cargo and baggage at remote airports without fancy high lift machines.


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What pattern of position lights did early Soviet jetliners use?
All aircraft that operate at night or in poor weather need position lights to make them visible to other aircraft for the purpose of avoiding mid-air collisions.  On most aircraft, these follow a set pattern: two continuously-illuminated lights on the wingtips (red on the left wingtip, green on the right [a pattern inherited from marine navigation lights], to allow other aircraft to see whether yours is flying towards or away from them), a continuously-illuminated white light in the tail, and high-intensity white anticollision strobe lights on each wingtip, in the tail, and on the upper and lower surfaces of the fuselage.
However, according to the Wikipedia article on the Ilyushin Il-62, early Soviet jetliners did not follow the standard arrangement for position lighting:

The Il-62 entered Aeroflot civilian service on 15 September 1967 with an inaugural passenger flight from Moscow to Montreal, and remained the standard long-range airliner for the Soviet Union (and later, Russia) for several decades. It was the first Soviet pressurised aircraft with non-circular cross-section fuselage and ergonomic passenger doors, and the first Soviet jet with six-abreast seating (the turboprop Tu-114 shared this arrangement) and international-standard position lights. [Emphasis added.]

What arrangement of position lighting did pre-Il-62 Soviet jetliners use?


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Why do the 747's wing gear tilt while airborne, but not its body gear?
The 747's sixteen main-landing-gear wheels are distributed over four bogies: two four-wheel wing gear, mounted underneath the inboard wings, and two four-wheel body gear, mounted under the fuselage further back.
When the aircraft is airborne with the main landing gear extended, the wing gear tilt upwards, while the body gear remain level:

(Image by Ian Kirby at airliners.net, via Wo st 01 at Wikimedia Commons.)
This is mentioned, but not answered, by this earlier question.
Given that the purpose of tilting the bogies is to reduce the longitudinal forces on the landing gear upon initial touchdown, it seems like it would make more sense to tilt the body gear as well as (or instead of) the wing gear, as - being further back on the aircraft - they are closer to the ground at positive pitch angles, causing them to touch down first and experience more-severe longitudinal touchdown loads, making the alleviation of these longitudinal loads more critical for the body gear than for the wing gear.
Why does the 747 tilt its wing gear instead of its body gear?

Video of 747 gear retraction
The body gear bogies are tilted, just not as much as the wing bogies, as a still from this video depicts. The difference in the bogie tilt seems more a function of retraction mechanism than of the placement - the wing gears tilt sideways, the body gears tilt forward. The amount of bogie tilt in combination with the retraction direction results in minimum space requirements once retracted.
Stills from the video:

Wing gear, sideways retraction

Body gear, forward retraction

I wondered whether different airflow below body and wings could have that effect.

@U.Windl They could, but the bogies just hang that way in the video as well, at standstill. They seem to be balanced that way, suspended by springs around the 4-bar retraction linkage.

The 747's main landing gear, as mentioned above, ALL tilt. The two wing gear tilt at a higher angle, I think about 53 degrees, if I remember correctly, and the body gear tilt around 8-10 degrees, I can't remember exactly now. (I flew the 747 aircraft for about 15,000 hours in all seats and types from the 747-100, -200, freighter, and -400.)
The main reason for tilting was to be able to fit these gigantic gear and wheel bogies into the wheel wells. In addition, the body gear which are behind the wing gear by several feet, help decrease turn radius on the ground. They turn in the Opposite direction that the nose gear does, so it scoots the tail end of the airplane around more quickly. This comes in very handy when maneuvering this monster plane in tight fits while taxiing on the ground.
IF any of the four sets of gear do not properly tilt to the proper angle after takeoff, you have a problem. You cannot safely retract the gear as it would damage the wheel wells and doors, and you will probably have to dump fuel and land back at origin or some other suitable airport.
Of course, one other advantage of the tilted gear for landings is that it helps provide a cushion for landing, and hard landings are reduced on this airplane, all other things being equal.
I think it was a marvelous airplane and I am honored I got to fly it for the majority of my airline career. It was truly "the Queen of the Skies" for a long time!

Welcome to Av.SE -- glad to have you here!

Oh, man, we have another Terry! :D Welcome and do please share your stories as you answer 747 related questions!!

Thanks, guys! I came across this website quite by accident, but glad I found it. I've been retired for almost 10 years now, but a lot of this knowledge is ingrained after so many years doing it. Happy to help out on future 747/aviation questions if I feel I know the correct answers.

"Happy to help out on future 747/aviation questions if I feel I know the correct answers" Well, you could start from here